The present invention generally relates to lampholders. More particularly, this invention relates to a vibration dampening lampholder for high intensity lighting structures.
Lighting structures experience various forms of vibration. This is particularly true for lighting structures located adjacent to bridges, roadways, railways and the like. Lampbulbs in such lighting structures are often damaged by the vibratory effects of passing vehicles, as well as wind loads and structure harmonics, which are usually low frequency, high amplitude vibrations. Lamp bulbs generally experience two types of damage from vibratory loads: shattering of the lamp envelope, and shattering of the lamp arc tube and other internal components. The various means known in the prior art for dampening the effects of vibration in lighting structures generally only succeed in reducing the shattering of the lamp envelope and then only to a limited extent. These prior art vibration dampening means are generally totally ineffective in preventing the shattering of internal components and may in fact facilitate damaging of internal components by directly transmitting vibratory loads from the lamp envelope to the brittle, spot welds utilized to fix the internal components of a lamp. Furthermore, lighting structures and the lamps disposed therein are subjected to vibratory forces from a variety of directions. The prior art vibration dampening means generally do not provide for omni-directional dampening of lateral, longitudinal and angular vibratory forces and therefore are further limited in their effectiveness. A still further limitation of the prior art dampening means for lighting structures is that they are generally unsuitable for use in the high temperature environs of roadway lighting structures which utilize high intensity lamps such as sodium, metal halide and mercury lamps. Lamp temperatures in such high intensity lighting structures may exceed 400.degree. F.
To dampen vibrations, various lampholders in the prior art include stiff metal supports and springs which engage the lamp envelope. A further exemplary prior art lampholder is illustrated in U.S. Pat. No. 3,908,878 to Crompton wherein there is shown a vehicle signal lamp that includes a bifurcated resilient member which telescopically receives a lamp socket for dampening of vibrations and mild shocks. In U.S. Pat. No. 4,176,391 to Kulik et al. a shock isolating lamp assembly for a vehicle lamp is disclosed that includes a resilient member which receives a lamp socket, the resilient member being formed having paired laterally-extending arms connected to respective mounting bars. U.S. Pat. No. 4,282,566 to Newman discloses a shock mounting bracket for a vehicle lamp bulb comprising a serpentine strip having a centrally located bulb-receiving socket which engages the base of the bulb. A conductive track circuit for a vehicle lamp bulb to protect the bulb from shock loads and vibrations is illustrated in U.S. Pat. No. 4,922,395 to Roney. The above-noted prior art references all disclose vibration dampening means limited by their engagement of a lamp socket or the base of a lamp bulb to reduce vibratory effects. These prior art references also do not disclose or suggest vibration dampening means for high intensity structures.
U.S. Pat. No. 3,671,923 to Rieth discloses a lamp socket that includes integrally-formed cantilever extension walls which support the envelope of a low intensity, wedge-type lamp bulb. In U.S. Pat. No. 3,676,834 to Kaldor et al. a vehicle lamp assembly is disclosed that includes an upwardly-extending resilient portion which grips the bulb envelope of a wedge-type bulb above its base for dampening of road shocks.
While the various prior art lamp vibration dampening means reduce vibratory effects to various degrees, certain limitations therein are overcome by the vibration dampening lampholder assembly of the present invention.